With development of small green lasers and blue semiconductor lasers using wavelength conversion elements in recent years, ultra compact projectors employing lasers as light sources have been proposed. Such a projector with laser light sources can demonstrate good color reproducibility and reduce the power requirement in a smaller package, and is implementable as a scanning-type image display apparatus that has various advantages; for example, it does not require affixed pixels and therefore can easily change the resolution.
For example, an ultra compact projector with laser light sources modulates the light sources for laser beams of three colors, i.e., red, green and blue, directly or indirectly through an external modulator, converts the laser beams into collimated light beams by collimation lenses, combines the laser beams into a light beam, and two-dimensionally moves the light beam on a screen using, for example, a MEMS mirror to project it as an image. In order to combine the laser beams of three colors, red, green and blue, on a single optical axis, dichroic mirrors are used as a well-known technique.
The technique of combining the red, green and blue laser beams on an optical axis with dichroic mirrors is disclosed, for example, in Patent Literature 1.
The projection-type display apparatus that combines red, green and blue laser beams into a single light beam and projects the light beam on an image-projected surface of a screen by using the combining technique disclosed in Patent Literature 1 needs to project the laser beams of respective colors to fill the same pixels on the image-projected surface to combine the red, green and blue laser beams into a single beam and project it onto the image-projected surface, which requires highly accurate adjustment of the optical axes of the laser beams of the respective colors. A conventional technique of adjusting the optical axes of the respective colors is known as, for example, Patent Literature 2. The technique disclosed in Patent Literature 2 is to reflect the respective laser beams with separate MEMS mirrors to perform a two-dimensional scan and provides a correction mechanism to each of the MEMS mirrors to correct an initial angle deviation.